I like that coil in the flue pipe Idea. I have copper tubing and lots of 4" flue pipe I have no use for. I may try this myself.
Something I was thinking about though maybe would help with the orginal post.
I will be heating water with my wood burner and an outdoor charcoal maker I am building instead of electric, but still hot water anyway.
In my trailer house the floor vents in each room are connected to a duct to an electric furnace in the center of the trailer. (I have Never used it!) I am thinking hot water radiator at the furnace, maybe use the condensor for the central air for this as it's alrady in place and just run hot water through it (I never use it either). Then I have hot air going into the duct at that point. Also run copper tubbing full of hot water through the existing duct, this keeps air hot and provides more heat on the way. Then at the air registers under the floor inside the duct, install small radiators such as used for car heaters, this provides more heat to the air right where it's needed as it exits the duct into the room.
I beleave that would work well. Just a hot radiator in my furnace I don't think would provide enough heat on it's own due to the high volume of air pushed by the blower at that point, but warming it there to begin with and also inline in the duct, I think it should be plenty warm at the room it heats.
Another thing I had thought of is just install the hot water radiators in the rooms and remove the furnace ducts under the floor. Build a little box around the radiators and install a small fan behind it. Just blow the cooler floor air through the radiator to heat it and warm the room, or better yet make a small duct and take the heat off the ceiling sucking it down to warm and re-enter at floor level.
Sort of like convection heat, forced air, and a ceiling fan all in one. Moving the hot air down from the ceiling helps alot, but my trailer cielings are to low to use fans.
I have had to use thoughs electric baseboard convection heaters before, and although they were a power hog, I liked them as far as heating the house then. Using water in the same way should work well but without the electric bill to follow!
My mother had hot water baseboard heat, worked by convection only (heating the rooms), was good, problem was the electric bill to heat the water!! ANY other way to heat the water and it would have been a good system, and thats a very large house!
Of course any type of hot water heat needs a hot water pump and that's been my hold up, finding one at a price I want to pay. Or even finding them at all, locally we have nothing here.
Anyway I think the water would be better than electric floor heat. First you either have to have electric when you want the heat, or batteries to store it for when you want the heat. Of course if the mills not spining a few days and the grid goes down (does that ever happen ) then that part of the system is down. With water heat a backup heater can be made that needs no real power other than the pump, so in an emergency like power outage you could use wood or propane/nateraul ect.. to heat water and the system is still working. Then a few batteries to power the pump or run a very small gennie as needed.
Floor heating sounds good, but I always think about when things don't work also! Electric blanket type floor heat may be ok off a mill if it works, but I think I'd only want it for suplimental heat and extra comfort and not actually count on it for anything myself. Kinda when it works great it's working, and when it's not, like oh well I don't really need it anyway, type of use.
Too many reasons for power to go out with the grid (and I expect it to get worse in future years, not better), though a mill doesn't worry about those reasons, but then a mill has other reasons to stop also. And does it ever go out on a nice, sunny, calm, warm, dry day?